Iran’s untraced mines in Strait of Hormuz: Why naval mines are difficult to detect

In any case, just hours after the ceasefire was announced, Iran again enforced its effective shutdown of the strait in response to Israel’s devastating strikes against Lebanon in alleged contravention of the truce.

What this reveals is that even if the ceasefire talks in Islamabad are successful, the presence of the mines could affect the normal flow of shipping traffic through the Strait of Hormuz for some time to come — potentially worsening the consequences for the global economy.

Finding naval mines is a challenge that has persisted since the World Wars. So why is it so difficult to locate them? We explain.

First, what are naval mines?

Naval mines are an old technology, with their use recorded as far back as the 14th century in China.

They are self-contained explosive devices placed in the water to destroy submarines and surface vessels. They are also used to deter access to certain areas or to quarantine an enemy in a specific location.

The first American sea mine was used during the American Revolution (1765-83). It was essentially a floating keg filled with gunpowder that exploded on impact.

Types of naval mines

Naval mines have come a long way since. According to the Robert Strauss Center for International Security and Law, sea mines may be classified by their methods of deployment, actuation or position in water.

Under the first classification, these methods may include surface boats, aircraft or even submarines.

The second classification depends on the extent of actual contact.

• Contact mines: As their name suggests, contact mines detonate when a vessel makes physical contact with (or otherwise comes close to) them in the water. These are the easiest to deploy.

• Influence mines: These technically advanced warheads do not require physical contact. They rely on sensors to identify specific target vessel characteristics or “signatures” — magnetic, acoustic, pressure, seismic, or underwater electronic signatures.

• There are also controlled mines, which may be detonated remotely.

The third classification of mines is based on their position in water.

• Drifting mines: These are placed in the water and move with the current.

• Moored mines: These are large, anchored ‘contact’ mines that  float just under the water’s surface. They release a hundred pounds of explosive force or more when they come in contact with a ship.

• Bottom mines: These are ‘influence’ mines that rest on the sea floor. As mentioned above, such influence mines use a combination of sensors to target a ship, exploding with hundreds of pounds of explosive force.

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• Limpet mines: These are small explosives that a diver can attach to a ship’s hull. It can be set to go off after a particular amount of time

Iran’s use of mines in the Strait of Hormuz

According to the US, Iran has about 5,000 to 6,000 naval mines. These include both contact mines (like moored and limpet mines) and influence mines (like bottom mines) which it can rapidly deploy in the Strait of Hormuz using high-speed small boats.

The Strait of Hormuz is a shallow waterway. According to a 1984 CIA document, declassified in 2009, much of the strait has a depth exceeding 45 metres, making it suitable for moored and bottom mines — both of which Iran possesses.

Iran’s semiofficial news organizations have recently published charts showing safe routes through the Strait of Hormuz. US Naval Institute

A Reuters report from mid-March said that Iran had laid about a dozen mines during this war, though it is unclear which varieties have been deployed.

While none of these may be powerful enough to sink a tanker on their own, they can cause significant damage.

Iran has mined the strait before. During the 1988 war with Iraq, it planted 150 mines in the strait. One moored mine, the SADAF-02, struck the American frigate USS Samuel B. Roberts in April 1988, nearly sinking it.

Why is it difficult to locate naval mines?

Let’s first take the case of land mines. They normally stay in place unless displaced by natural phenomenon such as flooding or earthquake. Even so, detecting them is difficult. For instance, farmers in France and Belgium still find unexploded ordnance from the first and second World Wars in their fields. Their annual collection is called the “Iron Harvest”.

In the case of sea mines, the challenge is even greater.

“The challenge with sea mines is that they can be laid in three layers: floating on the surface, floating inside the water or deployed to the bottom of the seabed. If they’re floating, they are vulnerable to tidal currents and can move location,” said Paul Heslop, an expert with the UN Mine Action Service.

An old-fashioned ‘contact’ mine. Wikimedia Commons

“You’re not only working in three different depths, so three dimensions, but also a fourth dimension, which is time. Over time, the mines may move. If an area is cleared, and there is a tidal surge or other current then that same area may be contaminated again. Moreover, some mines move through the water… so de-miners are working in a dynamic and changing environment,” he told UN News recently.

Drifting mines, for instance, could remain in the vicinity of the Strait of Hormuz for days, and could potentially pose a hazard after drifting into the Persian Gulf or Gulf of Oman.

In other words, these mines are easy and inexpensive to deploy, but difficult to remove.

But why would Iran not know where its mines are? According to the NYT report, Iran may have mined the strait haphazardly. It is not clear that Iran recorded where it put every mine. And even when the location was recorded, some mines were placed in a way that allowed them to drift or move, according to the officials.

Methods of removing naval mines

There are two broad methods to clear naval mines — minesweeping and mine hunting.

In the first method, a more old-fashioned one, specialised ships (or even aircraft) “sweep” for mines, dragging a wire or other equipment through the water to cut mine tethers and bring them to the surface to destroy.

In the second, more modern method, ships are specialized to “hunt” mines directly by using sophisticated sonar to detect them and remote vehicles to detonate them. There are vessels that are capable of both mine sweeping and mine hunting. Autonomous underwater vehicles can also scan the seafloor with sonar.

A minesweeping exercise by the Iranian Navy. Wikimedia Commons/FARS News Agency

Some countries also use drones to locate mines and then remote vehicles to detonate them. And other mines require sending divers in to neutralise them once identified.

According to the NYT, the US relies largely on combat ships equipped with minesweeping capabilities, rather than advanced technologies. Iran, too, does not have the capability to quickly remove mines.

Can the Strait of Hormuz be de-mined?

Completely clearing large naval minefields is a painstaking process. For instance, parts of some World War II naval minefields still exist because they are too extensive and expensive to clear.

According to another NYT report, after Iraq laid over a thousand naval mines in the Gulf in 1991, it took more than a dozen allied ships almost two months to clear the coast of Kuwait, averaging just over one mine a day. The technology has improved since then.

According to UN experts, dozens of sea mines deployed by Houthi rebels in the Red Sea during the Yemeni civil war can be a hazard to the busy shipping route for as many as 10 years.

The Persian Gulf region, including selected energy infrastructure. Photo: Iran Conflict and the Strait of Hormuz: Impacts on Oil, Gas, and Other Commodities; Congressional Research Service (2026)

But it is unlikely that Iran would have placed such massive numbers of mines. And it is also not necessary to scan every inch of the Strait of Hormuz or remove every single mine.

Heslop said: “If there is a peace deal or an agreement in the Strait of Hormuz and mines have been deployed, then for the foreseeable future, there will probably be a requirement, because of the dynamic nature of sea mines, to form a convoy and sweep for mines in front of that convoy.”

“A convoy would probably operate in a channel a couple of kilometres wide which has been cleared of mines. And obviously, depending on currents, tidal shifts, some areas are more likely to become re-contaminated than others,” he said.